The development of DNA-mediated gene transfer has provided an approach for the detection of cellular transforming genes. By using the NIH/3T3 transfection assay, transforming genes have been detected in diverse human and animal tumors, including sarcomas and hematopoietic malignancies. One approach toward identification of genes that may be preferential targets for somatic mutations leading to their acquisition of transforming activity involves analysis of animal tumor cells induced by specific carcinogens. Analysis of four methylcholanthrene-induced mouse fibrosarcomas demonstrated that two of these tumors are capable of transforming NIH/3T3 fibroblasts, that the acquired transformed phenotype is serially transmissible, that the transforming gene associated with these tumors is the same and is the cellular analog, c-kis, of the transforming gene of Kirsten murine sarcoma virus. These findings establish that c-kis is activated as a transforming gene at high frequency in these tumors. By using the same NIH/3T3 cell transfection assay, we also have sought to detect and characterize transforming DNA sequences of a spectrum of human hematopoietic tumors. We have detected in both acute and chronic myelogenous leukemia cells, as well as in acute human lymphoid leukemia cells, transforming genes capable of being serially transmitted to NIH/3T3 cells. The oncogene of one intermediate T-cell leukemia was demonstrated to be the activated human allele of c-kis, whereas two additional intermediate T-cell leukemias contained a different transforming gene related to, but distinct from, c-kis. This same gene was also found to be the transforming gene of one acute and one chronic myelogenous leukemia. Thus the NIH/3T3 transfection assay commonly detectes related oncogenes in human hematopoietic tumor cells. Moreover, the activation of these oncogenes appears to be independent of the specific state of cell differentiation or tumor phenotype.